Exfoliated MoS2 Nanosheet/Cellulose Nanocrystal Flexible Composite Films as Electrodes for Zinc Batteries

The study presents a more efficient way of exfoliating MoS2 in water and the exfoliated MoS2 was used in an electrode. The electrodes were prepared from exfoliated MoS2 (active material)–nanocrystalline cellulose (binder) with carbon nanotubes (electron-conducting support) and demonstrated in a zinc battery half-cell that showed a Coulombic efficiency of 90%. Successful exfoliation of MoS2 was done by sonication of bulk MoS2 with sulfated cellulose nanocrystals (CNC) for 4 h. The exfoliation was confirmed by Raman and transmission electron microscopy; interestingly, the Raman signals for exfoliated MoS2 show a blue shift for both A1g and E2g1 bands, which may be an indication of an induced lattice strain effect from the CNC on MoS2. The resulting stable water suspension showed no tendency of precipitation after 2 months of standing. The zeta potential, ζ, for sodium sulfated CNC (CNC–OSO3Na)–MoS2 in water suspension was −45 mV, whereas sulfated CNC (CNC–OSO3H)–MoS2 in water suspension had a zeta potential of −35 mV. The sodium form of sulfated CNCs displayed micelle characteristics, similar to sodium dodecyl sulfate (SDS), with a critical aggregation concentration (CAC) of 1.1 wt %. At CAC, the CNCs efficiently exfoliated MoS2, which is at a much lower concentration than has been reported for synthetic surfactants like SDS and cetyl trimethyl ammonium bromide.